From one teen heartthrob to another: Don't mess this up! Former '70s teen idol Leif Garrett spoke candidly with Fox News about his bad boy past in a recent interview, and the now 51-year-old singer and actor had a few key pieces of advice for current It boy Justin Bieber.

"Do not believe your own publicity," Garrett told FoxNews.com. "Sussing out who your real friends are is full-time work. Every scum bag, every drug dealer, every chicken hawk wants a piece of you."

And Garrett should know. At the young age of 8, the former child star hit it big in Bob & Carol & Ted & Alice, and went on to launch a top-10 single, "I Was Made for Dancin'," in 1979. Though his professional star was on the rise, however, the actor's substance abuse issues and run-ins with the law soon dominated headlines more than his actual projects.

"When you've got that sort of power at that young age, and everything at your doorstep, you put out that bad boy image," he explained. "At that age, testosterone, hormones, all of the money, you see what else you can get away with."

The parallels don't end there. During Garrett's hey day, the actor romanced former Desperate Housewives actress Nicolette Sheridan, and the pair often had a hot-and-cold relationship, not unlike Bieber's on-again, off-again relationship with Selena Gomez.

"[Bieber] rented out the [L.A.] Staples Center for [Selena]. Fame, money is what tore us apart," he said. "Nicolette just started modeling. My career was pretty much there. We would get along great or clear rooms. That's the whole thing with Justin and me. There was no in between … really good or really naughty."

In their defense, however, Garrett pointed out that both he and the 19-year-old "Believe" singer do contribute their fair share to charities.

Earlier this month, another Hollywood hunk similarly weighed in on Bieber's apparent teenage angst. In a live webchat with U.K. newspaper The Sun, Mark Wahlberg also offered his words of advice for the "Beauty and a Beat" singer.

"Justin, are you listening? Don't be so naughty, yeah?" Wahlberg quipped in a faux British accent. "Be a nice boy, pull your trousers up, make your mum proud, yeah? Stop smoking all that weed, you little bastard."